1. Field of the Invention
The present invention relates to an apparatus for and a method of processing a color signal inputted to a display, and more particularly, to an apparatus and a method that contribute to a color homogeneousness by obtaining an accurate channel control signal in response to an input color signal and use the obtained signal for a display.
2. Description of the Related Art
FIG. 1 shows CIE-xy color (chromaticity) coordinates. The CIE color coordinates are a two-dimensional graph having x and y axes. A hoof line 1 curved in a shape of a horse's hoof represents monochromatic waves of a visible spectrum that ranges from 360 nm to 830 nm. Colors included in the hoof line 1 are perceivable by human eyes.
Selecting two basic colors from an inside of the hoof line 1 at random and blending the selected colors results in a color lying on a line segment connecting two points which represent the selected colors on the CIE-xy coordinates. Selecting three basic colors from the inside of the hoof line 1 at random and blending the selected three colors results in a color lying within a triangle connecting three points that represent the selected three colors on the CIE-xy coordinates.
A conventional display system that has three primary colors, i.e., red (R), green (G) and blue (B), can only display the colors within the triangle connecting the RGB on the CIE-xy coordinates. Accordingly, such a display system cannot display natural colors outside the RGB triangle.
In order to solve the above-mentioned problem, a color processing apparatus having a new display system that has more than three primary colors was developed as disclosed in U.S. Pat. No. 6,262,744.
FIG. 2 is a view showing a conventional color driving method in a display system that has four primary colors (display primaries). Referring to FIG. 2, the display system having four display primaries R, G, B and D can only display colors within a convex polygon of RGBD.
That is, when the number of primaries (n) is 4, and when the number of channels k for a signal transmission to the display system is 3, the display system performs a color display by moving (switching) from the conventional display system containing three tristiumus values (X, Y, Z) to the new display system having four display primaries (R, G, B, D). After being coded in a coding process, each signal is transmitted through corresponding one of the three channels. In this case, each of the three channels transmits the signal of at least one primary color during the coding process, i.e., (n/k)=(4/3)=1. Next, since (n % k)=(4% 3)=1, one of the three channels transmits the signals of the two primary colors. Here, (n % k) is a remainder after dividing n by k.
When the four primary colors (R, G, B, D) are designated in the CIE-xy coordinates, a range of the display system having the four primary colors (R, G, B, D) is determined by points within a convex quadrilateral of RGBD. When the tristimulus values (Xi, Yi, Zi) are appropriately determined, the standardized CIE-xy coordinates can be calculated. That is, the CIE-xy coordinates are obtained by the following mathematical equation 1:
                                          x            i                    =                      (                                          X                i                                                              X                  i                                +                                  Y                  i                                +                                  Z                  i                                                      )                          ⁢                                  ⁢                              y            i                    =                                    (                                                Y                  i                                                                      X                    i                                    +                                      Y                    i                                    +                                      Z                    i                                                              )                        .                                              Equation        ⁢                                  ⁢        1            
Next, by substituting the CIIE-xy coordinates for the color coordinates of the displayed point (xi, yi) and the color coordinates of an auxiliary primary color D in the following equation 2, a location of a displayed point (xi, yi) is compared with that of the auxiliary primary color D:
                                          y            ′                    =                                    y              b                        +                                          (                                                                            y                      g                                        -                                          y                      b                                                                                                  x                      g                                        -                                          x                      b                                                                      )                            ×                              (                                                      x                    i                                    -                                      x                    b                                                  )                                      -                          y              i                                      ⁢                                  ⁢                              y            ″                    =                                    y              b                        +                                          (                                                                            y                      g                                        -                                          y                      b                                                                                                  x                      g                                        -                                          x                      b                                                                      )                            ×                              (                                                      x                    d                                    -                                      x                    b                                                  )                                      -                          y              d                                                          Equation        ⁢                                  ⁢        2            
where YR=0 when y′ and y″ are equal to or greater than zero (0), and YD=0 when y′ and y″ are less than zero (0).
Next, points (x1, y1) and (x2, y2) on the CIE-xy coordinates are obtained. Here, a point (x1, y1) exists within the triangle of three primaries B, G and D, and a point (x2, Y2) exists in the triangle of three primaries R, G and B. In other words, the point (x1, y1) exists on a left-hand side of a principal line GB (when y′ and y″ are equal to or are greater than zero), and the point (x2, y2) exists on a right-hand side of the principal line GB (when y′ and y″ are less than zero). Accordingly, driving signals to display the points (x1, y1) and (x2, y2) are obtained by the following equation 3:
                                                                                                                                                            1                        )                                            ⁢                                                                                          ⁢                                              Y                        D                                                              =                    0                                    ,                                                                          ⁢                                                            [                                                                                                                                  Y                              R                                                                                                                                                                                          Y                              G                                                                                                                                                                                          Y                              B                                                                                                                          ]                                        =                                                                                            [                                                                                                                                                                                          x                                    r                                                                                                        y                                    r                                                                                                                                                                                                                                    x                                    g                                                                                                        y                                    g                                                                                                                                                                                                                                    x                                    b                                                                                                        y                                    b                                                                                                                                                                                                                      1                                                                                            1                                                                                            1                                                                                                                                                                                                                          z                                    r                                                                                                        y                                    r                                                                                                                                                                                                                                    z                                    g                                                                                                        y                                    g                                                                                                                                                                                                                                    z                                    b                                                                                                        y                                    b                                                                                                                                                                                ]                                                                          -                          1                                                                    ·                                              [                                                                                                                                            X                                i                                                                                                                                                                                                        Y                                i                                                                                                                                                                                                        Z                                i                                                                                                                                    ]                                                                                            ⁢                                                                  ⁢                2                            )                        ⁢                                                  ⁢                          Y              R                                =          0                ,                                  ⁢                              [                                                                                Y                    D                                                                                                                    Y                    G                                                                                                                    Y                    B                                                                        ]                    =                                                    [                                                                                                                              x                          d                                                                          y                          d                                                                                                                                                              x                          g                                                                          y                          g                                                                                                                                                              x                          b                                                                          y                          b                                                                                                                                                1                                                              1                                                              1                                                                                                                                                    z                          d                                                                          y                          d                                                                                                                                                              z                          g                                                                          y                          g                                                                                                                                                              z                          b                                                                          y                          b                                                                                                                    ]                                            -                1                                      ·                                          [                                                                                                    X                        i                                                                                                                                                Y                        i                                                                                                                                                Z                        i                                                                                            ]                            .                                                          Equation        ⁢                                  ⁢        3            
Since display primaries R and D are non-coincident (mutually exclusive), the driving signals of the display primaries R and D are not simultaneously driven . In other words, the channel that transmits the signal of the display primary R to the display system also transmits the signal of the display primary D.
FIG. 3 is a view showing another conventional color driving method of the display system that has five primary colors. Referring to FIG. 3, n=5 and k=3, that is, the number of the display primaries (n) is five (5), and the number of the channels (k) is three (3). In this case, a transition is made from the conventional display system that has the tristimulus values (X, Y, Z) to another new display system having five display primaries. After being coded in the coding process, the signals are transmitted through the three channels, respectively. Here, since (n/k)=( 5/3)=1, each channel transmits the signal of at least one primary color during the coding process. Also, since (n % k)=(5% 3)=2, two of the three channels transmit the signals of the two display primary colors. The color range of the display system having the five primary colors R, G, B, D1 and D2 is determined by points located within a convex polygon of R, D1, G, D2, B.
Three principal primary colors R, G, B are selected from the five colors R, G, B, D1 and D2, and the two auxiliary primary colors D1 and D2 are selected such that D1 and D2 are evenly distributed among the principal primary colors R, G, B, that is, one auxiliary primary color is located between the two principal primary colors. For example, the auxiliary primary color D1 is selected to be located between the principal primary colors R and G, and the auxiliary primary color D2 is selected to be located between the principal primary colors G and B. The location of the point (x3, y3) and the location of the point (x4, y4) are obtained by using the selected D1 and D2 through the equations 1, 2 and 3. That is, resultant values of substituting the CIE-xy coordinates for a coordinate value of a point (x3, y3) in the equation of another line RG, and substituting a coordinate value of a point (x4, y4) in the equation of the line GB, are substituted in the equations 1, 2 and 3, to obtain the points (x3, y3) and (x4, y4).
As described above, a conventional color signal processing apparatus of the display system adopts the method of selecting and converting a transformation matrix that belongs to a range within the input color signals of the display primary colors R, G, B in order to obtain the channel control signal for a display. This method, however, requires hardware having a rather complicated circuit unit obtaining a (N−2) number of transformation matrixes if the number of channels N is is equal to or greater than 3. Further, since this method always reproduces a certain color signal through a combination of three signals, the display system does not have a color range that has the entire gamut of reproducible colors. Particularly, since the luminance of a display white has an intensity that needs three channels to be displayed at maximum, the display white by more than four primary colors cannot be obtained.